This invention relates to gyrotrons and more particularly to a high power high frequency gyrotron and gyro beam traveling wave tube amplifier (TWTA).
Prior art gyrotrons and amplifiers of the type which use a magnetron injection gun to provide a beam in which the electrons orbit about an axis which is the central axis of the gyrotron tube are limited in power handling capability and frequency at which they operate.
Prior art gyrotrons and amplifiers used an axial gyro beam to interact with a TE.sub.ml mode rf wave in a circular interaction cavity. The gyro electron beam was injected axially from an axially located electron beam source. The rf signal was provided to the interior of the circular interaction cavity by a circular waveguide and its rectangular-to-circular transition section which were located between the outer conductor of the cavity and the focussing magnet. A rectangular input waveguide was used to provide the rf signal to the transition section. The manner for injecting the input signal into the interior of the circular cavity is cumbersome and physical constraints make assembly of a prior art gyrotron more difficult. The amplified rf energy from the output of the circular interaction cavity must be separated from the axial gyrobeam. The techniques available resulted in substantial RF energy being transmitted along with the electron beam to a collector resulting in lower efficiency for the gyrotron. In a prior art attempt to attain the rf separation, a so-called miter-bend structure generated unwanted modes which tended to limit the practicability of the approach.
Proposed megawatt CW gyrotron designs at 100 GHz have considered several approaches which include the quasi-optical cavity, the higher order symmetrical circular waveguide mode (TE.sub.0n) interaction, the TE.sub.ml mode interaction, and multicavity interaction. Among these designs, the last approach may be adequate for achieving the megawatt goal at 100 GHz because difficulties with mode competition, ohmic heating and beam formation probably can be rendered tractable. Although remarkable progress has been demonstrated recently in achieving hundreds of kW CW power in the 60-100 GHz range, frequency and power extension of these gyrotron designs to meet the indicated goal seems nonetheless ambitious for reasons known to those skilled in the art.
It is therefore an object of this invention to provide an amplifier or an oscillator configuration of a gyrotron interaction device which is capable of providing higher power output and at a higher frequency than has been hitherto available by using the mode selectivity of the multi-stage cavity approach of this invention.